Electric annunciator drop



y 1948- F. A. STEARN 4 5 ELECTRIC ANNUNCIATdR DROP Filed Aug. 24, 1946INVENTOR.

QRANKLINASTEARN ATTORNEV Patented July 6, 1948 ELECTRIC ANN UN CIATORDROP Franklin A. Steam, East Newark, N. J., assignor to FederalTelephone and Radio Corporation, New York, N. Y., a corporation ofDelaware Application August 24, 1946, Serial No. 692,904

7 Claims. 1

This invention relates to electromagnetic signalling devices such asswitchboard drops and the like, and more particularly, to switchboarddrops of the visual magnetic type.

Signalling devices of the general kind to which this invention relateshave been in use for some time, and they usually comprise a target whichin displayed position is visible through one or more windowsconveniently placed in front of the operator. The target is mounted on apivoted armature which may be attracted by an electromagnet when thelatter is energized, and a restoring force such as gravity or a springmay be utilized to return the drop to its normal position afterdeenergization of the magnet. These drops are primarily useful where noaction of the operator is desired in response, and are widely used ontoll switchboards as self-effacing busy-indicators.

If it were desired to keep the device operated until the attention ofthe operator has been attracted, as in the case of call or clear-cutsignals, then the armature would have to be designed so as to be inequilibrium both in normal and in off-normal position. The difliculty ofmeeting this requirement accounts for the fact that in such circuits useis still made predominantly of the more conventional type of drops,employing a shutter and a latch-type armature, which are bulkier thanthe self-contained units of the so-called visual type and generallyrequire a correspondingly larger current for their operation.

It is therefore an object of the present invention to avoid theabove-mentioned dilficulties and to provide a compactly built, easilyinstalled magnetic signalling device of the non-restoring type, adaptedeither to display or to conceal a visible target, in either the operatedor the non-operated condition of the device, respectively.

In the accompanying drawing:

Fig. 1 is a perspective view of an embodiment of the present invention:

Fig. 2 is a fragmentary sectional elevation of the device shown in Fig.1.

An electromagnet I, having a core 2, is enclosed in an iron frame 3 andis connected to an associated energizing circuit (not shown). Anarmature l, pivoted in a bracket 5 which is mounted on the frame 3,carries the target arm 6 having a plurality of movable targets 1 securedto its front portion. The arm 6 may be of aluminum or other suitablelightweight material. A front plate 8, provided with a plurality ofwindows 9, is fastened to the frame 3 by the screws I0. Two permanentmagnets H and I2 are secured to the top and bottom portions of the frame3 and are magnetically insulated therefrom by brass bushings l3 and I4.Aligned with the magnets II and l 2 is a U-slraped magnetic latch memberI 5 which is rigidly attached to the target arm 6. An iron ledge l6,secured to the frame 3 by screws I1, is positioned underneath theleft-hand end of armature 4 and serves to complete the magnetic circuitthrough the core 2 and frame 3 when the armature l is in its attractedposition. Means are finally provided for the manual resetting of thearmature 4 to its normal position, these means being schematicallyillustrated as a push button l8 slidable in a hole 19 of frame 3.

When the right-hand end of the armature 4 is attracted by the core 2,upon energization of the electromagnet I, the targets 1 are aligned withthe windows 9 and are thereby visible to the operator. At the same time,the left-hand end of armature l rests on the ledge l6 and the lower endof latch member l5 preferably just clears the top of permanent magnet12. Preferably the armature carrying the target arm 6 and latch member15 is pivoted at a point close to the center of gravity of the combinedstructure. In this manner the energizing current of the electromagnetmainly has to overcome the force of the upper permanent magnet II whichis of predetermined strength, to display the signal. Although therestoring button I8 is illustrated as being manually operable, any knownautomatic resetting mechanism which can be initiated by the operator maybe used to return the device to normal. In such an event, again, therestoring force is principally determined by the field strength of thelower permanent magnet 52; thus relatively small forces may be employedfor this purpose. While only one embodiment of the invention has beenillustrated, it should be obvious to those skilled in the art that manymodifications and adaptations thereof may be made without departing fromits scope. Thus, some of its advantages might be realized even if one ofthe permanent magnets were omitted. Also, while the magnets H and l2have been shown as bar magnets, they could obviously be magnets ofhorseshoe or other suitable shape and could be arranged so that themember I5 completes an all-iron magnetic circuit when in thecorresponding position. Likewise, the pole pieces I! and I 2 could bethe ends of a single permanent magnet having, for instance, an extra legcommon to both magnetic paths. It is with these and similar equivalentsin mind that the scope of the present invention has been defined in theappended claims.

What is claimed is:

1. An electromagnetic signalling device comprising an electromagnet, anenergizing circuit for said magnet, an armature displaceable between anormal and an attracted position, signal means operable in one of saidpositions of the armature, magnetically susceptible means secured tosaid armature, and a permanent magnet magnetically insulated from theelectromagnet and positioned for magnetic cooperation with saidsusceptible means in one of said positions Of the armature.

2. An electromagnetic signalling device comprising an electromagnet, anenergizing circuit for said magnet, an armature displaceable between anormal and an attracted position, signal means operable in one of saidpositions of the armature, magnetically susceptible means secured tosaid armature, and two permanent magnets magnetically insulated frm theelectromagnet positioned for respective magnetic cooperation with saidsusceptible means in said two positions of the armature.

3. An electromagnetic signalling device comprising an electromagnet, anenergizing circuit for said magnet, an armature pivotabl'e between anormal and an attracted position, one or more targets secured to saidarmature, an apertured member having one or more windows positioned tobe aligned with said targets in attracted position of the armature, amember of magnetic material, non-magnetic means for securing said memberto said armature, and two permanent magnets positioned for respectivemagnetic cooperation with said magnetic member in said two positions ofthe armature.

4. A device as set forth in claim 3, an iron frame surrounding saidelectromagnet and said armature, and non ferrous means for mounting saidpermanent magnets on said inon frame in magnetically insulated relationthereto.

'5. An electromagnetic signalling device comprising an electromagnet, anenergizing circuit for said magnet, a frame of magnetic materialsurrounding a sufl'icient :portion of said magnet to provide asubstantially closed magnetic path therefor, an armature pivotablysecured to said frame and displaceable between a normal and an attractedposition, a non-ferrous arm carried by said armature, one or moretargets secured to said arm, an apertured member secured to said frameand having one or more windows positioned to be aligned with saidtargets in attracted position of the armature, a ferro-magnetic membersecured to said arm, and two permanent magnets mechanically secured tosaid frame and positioned for respective magnetic cooperation with saidfern-magnetic member in said two positions of the armature.

6. A device as set forth in claim 5, comprising an iron ledge secured tosaid frame and positioned underneath the end of the armature remote fromthe electromagnet so that said end rests on the ledge in the attractedposition of the armature.

7. A device as set forth in claim 5, comprising aniron ledge secured tosaid frame and positioned underneath the end of the armature remote fromthe electromagnet so that said end rests on the ledge in the attractedposition of the armature and simultaneously said ferrous memberjustclears the lower of said two permanent magnets.

FRANICLIN A. STEARN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number v Name Date 384,088 Scribner June 6, 18881,831,873 Miller 1 Nov. 17, 1931 FOREIGN PATENTS Number Country Date513,502 Great Britain Oct. 13, 1939

